A waste autoclave is a form of solid waste treatment that utilizes heat, steam and pressure of an industrial autoclave in the processing of waste. Saturated steam is pumped into the autoclave at elevated temperatures. The pressure in the vessel is maintained for a temperature-dependent period to allow the process to fully ‘cook’ the waste. The autoclave process provides an effective pathogen and virus kill.
The ‘cooking’ process causes plastics to soften and flatten, paper and other fibrous material to disintegrate into a fibrous mass, bottles and metal objects to be cleaned, and labels etc. to be removed.
Rotating waste autoclaves provide mechanical forces to further process the waste. With rotation, the cellulose fibers (in paper, cardboard, and yard wastes) are mechanically and thermally pulped, analogous to the process known as thermo-mechanical pulping in the pulp and paper industry.
After ‘cooking’, the steam flow is stopped and the pressure vented. When depressurized, the autoclave door is opened, and by rotating the drum the ‘cooked’ material can be discharged and safely and easily separated by a subsequent series of screens and recovery systems. Consequently, a waste autoclave system can serve as a functional alternative to landfills, providing benefits of recycling of clean and sterile materials recovered from municipal wastes.
A basic invention for municipal waste autoclaves is found in U.S. Pat. No. 4,540,495 (Holloway, 1985) and is now in the public domain which is hereby incorporated herein by reference.
The present invention represents an improvement over prior art apparatus and methods, such as those described in U.S. Pat. Nos. 5,540,391; 5,126,363; 5,253,764; 5,190,226; 5,361,994; 5,427,650; 5,407,809; 5,636,449; 5,655,718 and 6,397,492, all of which are hereby incorporated herein by reference. PCT application PCT/US06/16773 and co-pending patent application Ser. No. 11/716,101 are also hereby incorporated herein by reference.
The cost performance of an autoclave is driven predominantly by throughput, which in turn is determined by the density to which vessels can be loaded. Practitioners to date have used a variety of methods to load vessels, ranging from loose feed systems (e.g., conveyors) to light duty compression systems (compressing conveyors) to heavy-duty compression systems (compaction and load). Systems to date have not solved the core problem, which is to rapidly load an autoclave, preferably while rotating, with a designed or predetermined load of material.
In expansion of this core problem, MSW typically arrives on a “tipping” floor as a compacted mass. This compacted mass is broken apart and larger salvageable items are recovered. Waste materials expand in volume during the recovery.
In autoclave system processing, waste is moved by conveyor from the tipping floor to the processing floor. Waste may move more or less continuously after the tipping floor begins operations, while waste is charged into a vessel over a much shorter period. Thus, it is desirable to provide a “warehousing” activity and facility to store and accumulate waste over an hour or so, and then release it much more rapidly for load-out into a vessel.
Vessels are typically designed to operate within a 5-40% of full volume load range. Typically, an initial load will see significant volume reduction during vessel operations. Thus it is possible to compress the waste prior to or during the loading process, while still resulting in a partially filled vessel (on the basis of volume) after processing.
The economics of a system are driven by throughput. It is therefore desirable to operate a vessel near its upper design load, rather than near its lower design load. In order to achieve the upper design load, the load must be compressed prior to and/or during the loading process.
Prior practitioners have found pre-compression and/or in vessel compression difficult to achieve in practice because, once released from pressure, waste expands rapidly. Further, compression during the loading process requires significant time that could otherwise be used in waste processing.